Niemi has started all four San Jose games this season and has given up a total of five goals. The Sharks, meanwhile, have scored 21 times -- most in the NHL.
First-period goals by Marc-Edouard Vlasic and Matt Pelech put San Jose in charge. Mike Santorelli cut Vancouver's deficit in half midway through the second period, but Patrick Marleagu restored the Sharks' two-goal lead just 1:35 later. Brent Burns contributed an empty-net goal.
Vancouver had won three in a row after a season-opening setback. Roberto Luongo took the loss while making 25 saves.
Thomas Hertl, San Jose's rookie sensation who had seven goals in his first three games, was held scoreless while taking three shots.